As a far-infrared detector, a bolometer is generally used. The bolometer has an element for detecting a resistance change caused by heat; as such the bolometer is highly sensitive. However, since cooling by Peltier elements is necessary to maintain a constant temperature of the element, the bolometer consumes large amounts of power and becomes heavy when in a large form as a sensor. In addition, an S/N (temperature resolution) of a thermal image signal is likely to be affected by background radiation, and periodic calibration of each pixel with respect to temperature is necessary for the measurement. Therefore, a large-capacity memory is necessary, and in some instances, the acquisition of an image may be interrupted for calibration. With the special structure of a MEMS shape, the bolometer is not mass produced like a solid-state device. As a result, the bolometer has high power consumption, is expensive, large, and heavy. Therefore, there is a phenomenon wherefar-infrared ray detection does not occur and a realm for special use bolometers does not exist.
When using the principle of photoelectric conversion which is commonly used for visible ray detection for far-infrared rays detection, it is possible to use a solid element formed of a semiconductor or the like. However, since the energy of the far infrared rays (wavelength about 10 micrometer) is as small as 120 meV, it is necessary to cool the solid element to the temperature of liquid nitrogen or below.
As an imager for photosynthesis use using a field-effect transistor (FET), the imager performs imaging by being connected to a photosynthesis center using the molecular wire on a gate electrode, and modulating a gate potential using photoexcitation potential of photosynthesis in light reception (for example, refers to NPL 1).
However, since a detection wavelength is limited to a wavelength at which bio-molecules can photosynthesize in the imager, the detection wavelength is limited to a single wavelength of visible rays and far-infrared rays may not be detected. In addition, this imager includes a solution system and uses bio-materials, thereby having low durability.
Photoexcitation potential is small, sensitivity is low, and an S/N ratio is also small.
Several far-infrared ray sensors of the spatial light modulation type have also been proposed (for example, refer to NPL 2, PTL 1 and 2). The spatial light modulation type is a method for obtaining a thermal image by detecting a temperature change of dielectrics due to absorption of far-infrared rays through changes in the dielectric constant.